How things have changed since Barcelona beat PSG 6-1

Barcelona and Paris Saint-Germain meet again in this season's Champions League last 16, and it's not a fixture without its history.

This tie will forever be synonymous with that night at Camp Nou in March 2017.

Luis Enrique's side kicked off the second leg of their tie against PSG at the same stage of the competition four years ago with an absolute mountain to climb.

Goals from Julian Draxler, Edinson Cavani and a double from Angel Di Maria at Parc des Princes just three weeks earlier had seemingly assured the Parisians of their passage through to the quarter-final stage of the competition.

Barça would need to produce the biggest comeback in Champions League history if they were to progress, and while Lionel Messi's 50th minute penalty had home fans dreaming with the aggregate scores at 4-3, Cavani's sucker punch just past the hour mark all but extinguished their feint hopes.

But Barcelona just don't do boring.

With two minutes of normal time remaining, Neymar struck twice meaning Enrique's men required just one more goal to complete mission impossible, before Sergi Roberto's 137th minute (or something like that) decider sparked pandemonium inside Camp Nou.

The two sides meet again in the first knockout round of Europe's premier competition on Tuesday evening, and it's fair to say quite a bit has changed since their 2017 duel.

Now, that might sound like a stupid thing to say - it was four years ago, of course things have changed - though few could have envisaged Barcelona would be in the turmoil they find themselves in right now.

The Spanish giants where forced to embark on a fire sale of their hottest properties over the summer in a bid to generate cash, with reports claiming the club are struggling to repay €900m (£804m) of debt.

Said sale saw the departures of some stellar players - most of which were free transfers - including Arturo Vidal, Ivan Rakitic and Luis Suarez, with the latter inexplicably sold to La Liga rivals Atletico Madrid where he looks destined to fire them to their first Spanish title since 2014.

Ronald Koeman has threatened to implode just about every time he's had a microphone shoved in front of him this season, with not even the club's hierarchy immune from his criticism - probably not the best idea when you're eight points off the league leaders and they've got two games in hand over you.

Meanwhile, PSG have gone from strength to strength since their collapse in 2017, with Kylian Mbappe added to their ranks and establishing himself among the world's elite, and their Camp Nou tormentor Neymar swapping La Liga for Ligue 1.

Not only have PSG added plenty of flair to their squad over the past few years, they also look a far more solid outfit than the team that crumbled in Catalonia four years ago, and their steady progression has seen them notch three consecutive French titles as well coming within 90 minutes of being crowned Champions League winners last summer.

That being said, there are still areas of their squad which need addressing, with a number of high-earners being afforded little game time and needing to be moved on.

The departures of Thiago Silva and Cavani have afforded the opportunity to add youth to the squad - something which is also badly needed - and the appointment of Mauricio Pochettino may well have been driven by that very need.

All of the above seems to suggest that this last 16 encounter is going to be a walkover for the French side - yet, we of course know that isn't the case.

Despite being a team in transition, PSG's current squad contains a number of players present for their 2017 collapse, leading to suggestions they could suffer some sorta weird four-year hangover when they face Barcelona on Tuesday night.

However, Pochettino refused to accept the previous meeting could have any possible impact on the outcome of the upcoming tie, and he believes PSG have come a long way since their disastrous night in Barcelona.

"I'm calm and chilled, as this [PSG] are a different team," Pochettino told reporters as quoted by Marca.

"What happened can't be erased, but we want to build another future, and all of us always [want] to build something better than what happened."

It's not so much a case of sliding doors with these two sides, as that would imply that Barcelona have slowly regressed - the 'Barcelona door' has effectively fallen off its hinges.

However, it would be amiss to ignore the fact the two clubs are heading in total different directions, with one looking to recruit some of the biggest names in world football, and the other asking their rivals to take their best players off their hands as they can't afford their wages.

Their round of 16 tie won't just determine which team advances to the quarter-final stage, it will give an insight into where these two sides are at. One an emerging powerhouse of European football, the other looking set to earn the tag of 'fallen giant'.